Fluid operated brake



Sept. 16, 1941. R. c. HOYT FLUID OPERATED BRAKE Filed Sept. 20, 1955INVENTOR. /Wf 7- Mja/ffm ATTORNEYS.

IPatented Sept. 16, 1941 UNITED STATES PATENT OFFICE 2,255,974 FLUmoPERATEn BRAKE Roy C. Hoyt, Duluth, Minn. Application september 20,1935,serie1No.41,391

(Criss- 152) 7 Claims.

My invention relates to fluid operated brake, for automobiles and forsuch other vehicles and mechanisms as it may be adapted to serve. It hasfor an object the provision of fiuid-operated braking means in which theuid is adapted to automatically compensate for wear of the brake shoelining. With this and other objects in view, it consists ofthestructures, combinations and arrangements of parts hereinafterdescribed and claimed.

In the drawing, Fig. 1 is a section of my invention on the line I-I ofFig. 2. Fig. 2 is a view of my said invention with some parts shown inside elevation and some parts sectioned on the line 2-2 of Fig. 1.

In the drawing, I is a relatively stationary or non-rotatable back plateconcentric with a vehicle wheel (not shown), and 2 is a brake drum alsoconcentric with such wheel and secured thereto in any suitable manner,as by bolts (not shown), projected through bolt holes 28L in said drumand through any suitable part of such wheel. Between said drum and backplate and pivotally connected at their heels to said back plate, is apair of segmental brake shoes 3, each of which extends in an arcapproximately concentric with the said drum. The pivots 3 of `said shoesare, preferably, a trifle eccentric,

fianged sealing cups 6, inward of each of whichV sealing cups 6 ispositioned in said cylinder a press fit stationary sleeve 1. Workingwithin each stationary sleeve 1 is an outwardly flanged sealing cup 8.These sealing cups 8 serve as check valves, and each thereof cooperatesand moves with one of a pair of piston-like valve bodies 9. The sealingcups 8 seat against the closed outer ends of their respectivecooperating valve bodies 9, which valve bodies l9 are free to moveaxially between limits established by engagement of theirfianged innerends with cooperating axially spaced stop shoulders I3 and I4, and hencemay. be termed floating valve bodies. The space in the central portionof cylinder between the fioating valve bodies 9 serves as an intakechamber Il for receiving operating fluid conducted to it from anysuitable source by any suitable means, as byport 4b and pipe I0.

Said sealing cups 6 are adapted to be forced closely against the wallsof said cylinder by fluid pressure inwardly thereof, but arereciprocable within said cylinder, being adapted to be moved outwardlyby uid pressure from below and to thus push outwardly the shoe operatingpistons 5 and the toes of the brake shoes resting upon them, and beingadapted to be moved inwardly by the pressure of said pistons 5 and shoes3 under compression by the hereinafter described springs II when thepressure fromv below is reduced.

Said valve bodies 9 have ports 9a formed'therein for the passage offiuid from the intake chamber l under conditions hereinafter described.

The fixed sleeve 'l is provided in its head with ports 1 for the passageof fluid in either direcion.

The check valve-acting sealing cups 8 are adapted to contractsufficiently Ato permit leakage, around their peripheries, of fluid fromthe intake chamber 4B, but to expand suiciently to prevent return ofsuch fluid, when the pressure in the intake chamber is reduced. They,also,

are reciprocable within said cylinder, being f adapted to be movedoutwardly by the valve bodies 9 and inwardly by fiuid under springpressure outwardly thereof when the pressure in the intake chamber isreduced.

The means for applying the operating pressure to the fluid in thecylinder may be a footactuated piston (not shown, but well known to theart), foro ed against the fluid in said pipe,- the pressure beingreleased by withdrawal of the operators foot. Means for applyingretracting pressure to the reciprocable parts and fluid in said cylindercomprises contracting springs II each secured at one end to any suitableanchorage, as to a pin Ia on said back plate, and at its opposite end t0one of said shoes to retract the toe ends of said shoes, whichby reasonof their bearing upon the pistons 5--force back their cooperatingreciprocable parts'and fluid in said cylinder inwardly thereof.

Upon each of said shoes is preferably secured alining 3c (of anysuitable material) adapted to contact with the inner face .of a fiange2b, forming part of said drum, when said shoes are moved to operativeposition, in opposition to said springs II, by iiuid pressure inwardlyof the pistons, respectively.

It will be observed that a quantity of fluid is normally trapped betweenthe sealing cups 6 and l 8. As the lining of the shoes becomes worn,

more trapped uid is necessary to force the shoes l and passages betweensaid sealing cups 8 and 8 until such space is full when said shoe is inoperative position. Thus the wear of the brakeshoe lining will becompensated by the gradual increase of fluid-filler between saidgaskets.

In the drawing the several reciprocable partsv of the double brakemechanism heretofore described are shown in their normal inoperativeretracted positions, where they are automatically compensate for thevery slight wear produced-by -A the preceding braking period. Inthevdrawing .there is a very decided clearance shown between the headsof the sealing cups andthe interior of the lstationary sleeves 1 inorder to make the Afollowing of the fluid path easy, but in practicetional fluid will pass out, under pressure, through l the ports 9a andleak past the peripheries of thevalve-acting sealing cups 8 into thetrap-space moved and retained in the absence of brake setting pressurein the intake chamber4a by the retracting springs II. It is importantto'note that in this inoperative retracted position of the 1 severalparts the oating valve 4bodies 9 are in their inner extreme positionedwith their flanges seated against the stop shoulders I3, said valvebodies being maintained, under this condition, in their inner extremepositions by the columns of fluid compressed between their respectivecheck valve-acting sealing cups 8 and their cooperating brake shoeoperatingsealing cups'S-yunder the action of the springs II.

When it is desired to set the brake, additional fluid will be forcedinto the cylinder intake charnber 4 through the pipe I0 and port 4b, andthis additional fluid in the intake chamber Iand the resultant increaseof pressure in the intake chamber will initially produce a substantiallysimultaneous outward movement of all of the reciprocable parts inclusiveof the floating valve bodies 9, sealing cups 6 and 8, actuating pistonsand the brake shoes. Outward movement of the floating valve bodies 9with the expanding column of fluid is the result of the relatively greatresistance to passage of uid through the small ports l)EL therein andaround the peripheries of the head portions thereof. Outward movement ofthe floating valve bodies 9 with the column of the uid is, of course,limited by engagement of the flanges thereof with their respectivecooperating stop shoulders I4 at which time it is important to note thatthe valve-acting sealing cups 8 thereof engage and are stopped againstfurther outward movement by the inpressed axial portions of the heads ofthe press fit stationary sleeve 1. If, when the floating valve bodies 9and their respective cooperating valve-acting sealing cups 8 havereached their outer extreme positions the brake shoe linings have notyet come into full braking engagement with the brake drum, continuedbrake setting just normal working clearances are sufficient, due

to the exceedingly small and almost infinitesimal amount of fluid passedby the floating valve bodies during any one braking operation.

When the uid pressure in the intake chamber 4" is relieved to releasethe brake, the several reciprocating parts inclusive of the free or toeend portions of the brake shoes, the actuating pistons and their sealingcups 6 and the floating valve pistons 8 and their respective cooperatingsealing cups 8 and the quantity of fluid entrapped between cooperatingsealing cups 6 and 8 move inwardly under the retracting pressure ofsprings II to the extent permitted by an engagement of the flanges ofthe valve bodies 9 with the stop shoulders I3 at which time the saidseveral reciprocating parts come to and remain at rest, further movementof the actuating pistons 5 and their sealing cups 6 and the entrappedcolumns of fluid being prevented by the valve-actingsealing cups 8 whichpermit flow of fluid in an'outward direction, but positively preventflow of the fluid therepast in an inward direction. Hence, it will beseen that the free or toe end portions of the linings or facings 3 ofthe brake shoes are always retracted to, at the end of a `braking periodand remain between brake setting periods in, positions a definitedistance from the drum so that. regardless of the stage of wear of thebrake shoe facings and engaged surfaces of the brake drum, whichconstitute together the friction surfaces of the brake. The said toe`end portions of the brake shoe facings will always be positioned betweenbraking operations in exactly the desired spaced relation to the drum,and this of course without requiring any manual adjustment whatsoever.It will be seen that between braking operations the springs I Iactingthrough the brake shoes and their cooperating pistons 5 willmaintain the columns of fluid entrapped between the cooperating sealingcups 6 and 8 unA der sufliciently greater pressure than is then existingin the intake chamber 4 to maintain the flanges of the sealing cups 6and 8 in positive sealing engagement with their cooperating cylindricalsurfaces. The valve bodies 9 and their cooperating sealing cups 8 serveas fluid release measuring valves.

What I claim and desire to secure by Letters Patent is- 1. A cylinderfor hydraulic brakes having a l medial wall and a chamber on each sideof said pressure in the intake chamber l will cause fluid from saidchamber 4 to seep through the small portsv 9a in the floating valvebodies 9 and -pastthe valve-acting sealing cups 8 in an out- Warddirection, thereby increasing the length of between-the sealing cups 6and 8 sufficiently to 75 wall, a perforated cup member positioned oneach side of said wall, a flexible valve in each cup member, a pistonseal in each chamber vand a piston operable by said pistonseaL 2. Abrake having friction elements comprising a brake drum and a brake shoemovable toward yand from said drum, actuating means to move the shoeinto engagement with the drum..

limiting means to maintain a constant clearance between shoe and drum,said shoe actuating means comprising an independent'. actuating pis-- Yton mounted in a cylinder and provided with a fluid seal, said limitingmeans Aconsisting of a the latter said oating piston being provided witha combination fluid seal and iiuid check valve for facilitating thetrapping of fluid between the two pistons, thereby defining andmaintaining the pistons adjustedat a distance corresponding to a desiredclearance between the friction elements, while said actuating piston isinactive, and means for normally keeping the trapped fluid between thepistons under pressure so as to urge the uid seals of both pistons intosealing contact with their common cylinder wall. Ii

3. A brake having friction elements compris'- ing a brake drum and abrake shoe movable'toward and from said drum, fluid actuated means formoving the shoe into engagement with the drum, limiting means torestrain the movement of the shoe away from the drum to maintain aconstant clearance between said shoe"and said drum when said iiuidactuated means is inactive, said shoe moving and said -limiting meansincluding two independent hydraulic pistons, individually operative andaligned in 'a common cylinder, both pistons having fluid sealing gasketsarranged so as to facilitate the trapping of fluid between the pistons,the gasket of the piston of said 'limiting means serving as a onewayfluid 'check valve, operable towards the space confined between thepistons and preventing the escape of fluid trapped therein, and pistonmovement limiting means provided at the end of the piston remote fromthe space conned between the two pistons, for limiting its intendedmovement in either direction, tension means associatedu with the brakeshoe and adapted to normally keep the fluid trapped between the pistonsunder pressure.

4. In a fluid brake system comprising a drum, friction meansco-operative with said drum, actuating means located in said drum andfluid pressure adjusting means for adjusting the friction means tocompensate for wear, said actuating means and said adjusting meanscomprising a pair of independent, bodily separated pistons, aligned withone another and cooperative in a common cylinder and said adjustingmeans comprising an annular piston seal cooperative with the bore ofsaid cylinder and arranged to by-pass duid in one direction.

5. A iiuid operated braking system comprising a brake drum, a pair ofbrake shoes, aA pull back spring for said-shoes and an operating wheelcylinder, all positioned within said drum, said wheel cylindercontaining two aligned brake shoe actuating units each comprising afloating piston in operative engagement with one of saidshoes and asecond floating piston coaxial with the rst mentioned piston and havingmeans for limiting its stroke in each direction, said second floatingpiston having an annular piston seal arranged to pass uid to the firstpiston when the brake is applied and to otherwise retain iiuid betweenboth pistons under pressure responsive to said pull back spring.

6. A iiuid operated braking system having a master piston to providefluid pressure and a brake actuating piston responsive to said iuidvpressure, and comprising a floating piston having a limited stroke andinterposed between the master piston and the brake-actuating piston,

to said actuating piston to effect an automatic brake adjustment whenthe brake is applied, and is otherwise retained between said brakeactuating piston and said floating piston to maintain said brakeadjustment.

'7. A brake having friction elements comprising a brake shoe cooperativewith a brake drum, a pull back spring for said brake shoe, ,and ahydraulic cylinder for said brake, said cylinder having a brakeactuating unit comprising a floating piston in operative engagement withsaid shoe and a second oating piston coaxial with said first mentionedpiston and lhaving two-way means for limiting its stroke in each of twoaxial directions, and limiting means being positioned on a side awayfrom 'saidflrst mentionedy shoe when the brake is applied, and tootherwise retain uid between said pistons under pressure responsive tosaid pull back spring for maintaining said adjustment. v

ROY C. HOYT.

